Network device with optical communication interface

ABSTRACT

Embodiments of the present disclosure include optical transmitters and transceivers with improved reliability. In some embodiments, the optical transmitters are used in network devices, such as in conjunction with a network switch. In one embodiment, lasers are operated at low power to improve reliability and power consumption. The output of the laser may be modulated by a non-direct modulator and received by integrated optical components, such as a modulator and/or multiplexer. The output of the optical components may be amplified by a semiconductor optical amplifier (SOA). Various advantageous configurations of lasers, optical components, and SOAs are disclosed. In some embodiments, SOAs are configured as part of a pluggable optical communication module, for example.

CROSS REFERENCE TO RELATED APPLICATIONS

The present disclosure related to concurrently filed U.S. patentapplication Ser. No. 16/938,581.

BACKGROUND

The present disclosure relates generally to optical communications.

An important application of optical communication is in computernetworks connecting servers and storage systems in large data centers.For example, the majority of all network traffic today is generated byservers inside of large Cloud Data Centers that are connected to eachother and to the Internet with high-speed Data Center Switches.

The throughput of network switches continues to grow at a significantrate with the next generations of network switch chips providingthroughput of 51.2 Tbps (Terabits per second). Such switch chips requirea large number of lasers for optical communications.

One problem with today's high-speed optical communications is power andreliability. Today's optical communication modules use high power laserwith high current densities that reduce the expected lifetime of thelaser and thus the meantime between failure.

Another problem with today's high-speed optical communications is thatthe reliability is insufficient for using optical communications withinthe chassis since an optics failure would require a complete chassisreplacement. To enable optical communication within the chassis,including so-called “co-packaged optics” (CPO) the reliability of theoptics components would need to improve by at least an order ofmagnitude.

Various embodiments described herein reduce the power and to increasethe reliability of optics communication for high-speed datatransmission.

BRIEF DESCRIPTION OF THE DRAWINGS

With respect to the discussion to follow and in particular to thedrawings, it is stressed that the particulars shown represent examplesfor purposes of illustrative discussion, and are presented in the causeof providing a description of principles and conceptual aspects of thepresent disclosure. In this regard, no attempt is made to showimplementation details beyond what is needed for a fundamentalunderstanding of the present disclosure. The discussion to follow, inconjunction with the drawings, makes apparent to those of skill in theart how embodiments in accordance with the present disclosure may bepracticed. Similar or same reference numbers may be used to identify orotherwise refer to similar or same elements in the various drawings andsupporting descriptions.

FIG. 1 illustrates an optical transmitter.

FIG. 2A illustrates an optical transmitter according to an embodiment.

FIG. 2B illustrates a comparison of power consumption.

FIG. 3A illustrates an example optical transmitter with pluggable SOAaccording to some embodiments.

FIG. 3B illustrates another example optical transmitter with pluggableSOA according to some embodiments.

FIG. 4 illustrates a network device including a pluggable SOA moduleaccording to an embodiment.

FIG. 5 illustrates an example of a co-packaged module coupled topluggable SOAs according to another embodiment.

FIG. 6 illustrates an example of multiple pluggable modules according toanother embodiment.

FIG. 7 illustrates a network device with an integrated optics moduleaccording to an embodiment.

FIG. 8 illustrates a network device with pluggable optics according toanother embodiment.

FIG. 9 illustrates an example configuration of printed circuit modulesaccording to an embodiment.

FIG. 10 illustrates an example configuration of printed circuit modulesaccording to another embodiment.

FIG. 11 illustrates an example configuration of printed circuit modulesaccording to yet another embodiment.

FIG. 12 illustrates an example power link budget estimate according toan embodiment.

FIG. 13 illustrates an example network device including opticaltransceivers according to an embodiment.

FIG. 14 illustrates another example network device with pluggableoptical components according to an embodiment.

FIG. 15 illustrates another configuration of lasers and semiconductoroptical amplifiers according to another embodiment.

FIGS. 16A-B illustrate another network device with pluggable opticsaccording to an embodiment.

DETAILED DESCRIPTION

Described herein are techniques for optical transmitters and opticalcommunication systems. In the following description, for purposes ofexplanation, numerous examples and specific details are set forth inorder to provide a thorough understanding of some embodiments. Someembodiments as defined by the claims may include some or all of thefeatures in these examples alone or in combination with other featuresdescribed below and may further include modifications and equivalents ofthe features and concepts described herein.

FIG. 1 illustrates an optical transmitter, which may be included as partof a transceiver in some embodiments. Contemporary optical transmittersmay include a laser 101 coupled to a fiber optic cable 103 throughoptical components 102 (e.g., multiplexers, modulators, and the like).Laser 101 may be a laser diode, for example. One fundamental challengefor some laser based optical communication systems is the reliability ofthe laser diodes, which may be the most common failing component insidean optical transceiver. Reliability levels of electronic and photonicsdevices are typically measured by FIT (failure in time) or MTBF (meantime between failures) for systems and subsystems. Reliability can alsobe measured by MTTF (mean time to failure) for components. The term FITis defined as a failure rate of 1 per billion hours. MTBF is equal to 1divided by FIT.

For example, some contemporary optical transceivers running at highbandwidth are 400 Gbps transceivers typically using four differentoptical channels running at 100 Gbps with a PAM4 modulation scheme. Fora network switch with 51.2 Tbps bandwidth, there is a need for 512 diodelasers to support 512 100 Gbps channels. Assuming MTTF of a single laserdiode of 10,000,000 hrs., the MTBF of the entire system may be less than20,000 hrs., not taking into account potential failures of all otherelectronic and photonic components. Such a failure rate is notsatisfactory for large data center applications.

An additional challenge of some optical communication systems is thehigh power density generated by electronics and photonics devices. Forexample, the overall power of a 51.2 Tbps switch chip and relatedcomponents for optical transmission packaged on one board is projectedto exceed 1 kW, resulting in high component temperatures. Hightemperature has a negative exponential effect on the lifetime ofsemiconductor devices, including lasers. The same is true for an opticaltransceiver with high bandwidth because the power may have to bedissipated in a relatively small volume.

Features and advantages of the present disclosure include an opticaltransmitter (or transceiver) including a laser coupled to asemiconductor optical amplifier (SOA). In some embodiments, a laser maybe operated at lower power and current density levels to improvereliability. The output of the laser is coupled to a fiber through theSOA to achieve the appropriate amount of power at the fiber input. Insome example embodiments, the SOA may be pluggable, such thatreliability issues may be shifted to the SOA which can be easilyreplaced, for example. Additional example embodiments are illustratedbelow.

To transmit optical signals over optical fibers for a certain distance,a certain light power must be generated by the laser. A typical designof an optical transceiver and laser power levels are shown in FIG. 1 .Here, a laser 101 generates an optical signal, which is coupled throughoptical components 102 (e.g., multiplexers and/or modulators). Theoptical signal is then coupled to a fiber optic cable 103 fortransmission (receive path not shown). Laser power of laser 101 may beset by a link power budget because there are various losses within theoptical components 102 in the optical path: from the laser transmitter(Tx) in the first module in the link to a photodetector in the receiver(Rx) in the second module of the link (not shown). These losses includeinsertion losses of light from the laser to all photonics elements onits path and attenuation within fiber optic cable 103. For example, atthe current level of development of some optical component and lasertechnologies the overall loss of laser light going through opticalcomponents 102 may be above 15 dB, resulting in a requirement togenerate about 30 mW of optical output laser power for one channel. Thispower may be achieved at about 120 mA drive current, for example. On theother side, the maximum length of a laser strip may be limited to 1-2 mmdue to the presence of internal losses in the laser waveguide caused byfree carrier absorption. This reduces differential efficiency for longerdevices. In such a design the typical drive current density of somelasers 101 used conjointly with optical components 102 may be above8,000 A/cm², significantly exceeding the threshold current density whichis typically below 500 A/cm².

Failure rates of semiconductor lasers strongly depend on p-n junctiontemperatures, optical power densities, and drive current densities. Thetypical formula for failure rate vs temperature, optical power, anddrive current for the laser of a given size is as follows:

${F\left( {T_{j},P,I} \right)} = {F_{op} \cdot {\exp\left( {{- \frac{E_{A}}{k_{B}}}\left( {\frac{1}{T_{j}} - \frac{1}{T_{op}}} \right)} \right)} \cdot \left( \frac{P}{P_{op}} \right)^{n} \cdot \left( \frac{I}{I_{op}} \right)^{m}}$

where the function F is the failure rate (and MTTF (hrs.)=1/F), F_(op)is a certain value of failure rate at certain p-n junction temperature,T_(op), light power, P_(op) and drive current I_(op), T_(j) is p-njunction temperature, P is laser optical power, I is laser drivecurrent, k_(B) is the Boltzmann constant, E_(A) is the Arrhenius factor(activation energy), n is exponential optical power acceleration, and mis exponential current acceleration. Both optical power and currentstimulates the formation, growth and propagation of non-radiativedefects resulting in the degradation of laser power e.g. dark linedefects or catastrophic optical mirror damage, or defects. For varioustypes of semiconductor lasers, the sum of exponential accelerationfactors “n” and “m” typically exceeds 4. Following the equation above,one can estimate for the set of 512 lasers mentioned earlier, which hasan aggregated MTBF of 20,000 hrs. at the drive current and powerrequired by a link budget in an example operating application in anoptical network system, such as a data center, the MTBF would be atleast 625 (5⁴) times higher if the lasers are driven at 5 times lowerdrive currents. In this case the overall MTBF would be equal to12,500,000 hrs., far exceeding current market acceptance levels.

Thus, certain embodiments of the present disclosure may run diode lasersat lower current densities from reliability and power consumption pointsof view, for example. For instance, the laser may be operated at a lowpower level corresponding to a reliability above a target threshold, forexample. However, due to the presence of optical loss in the linkincluding fiber attenuation, coupling loss, insertion loss of thereceiver and others, the system may be required to deliver certain levelof light power into the fiber on a transceiver side in order to achieveacceptable BER (bit-error-rate) at a given sensitivity of photodetectoron the receiver part.

FIG. 2A illustrates an optical transmitter according to an embodiment.Optical transmitter 200 includes laser 201, optical components 202,optical connector 205, and a semiconductor optical amplifier (SOA) 203having an output coupled to a fiber optic cable 204. In variousconfigurations, data may be converted from electrical signals to opticalsignals by driving the laser indirectly (e.g., via electro-absorptionmodulation) or by driving optical components 202 (e.g., integratedsilicon based optical modulators). Non-direct modulation may improve theability of a laser 201 to be operated at a low power, for example. Amodulated optical signal may be coupled to a semiconductor opticalamplifier 203, which boosts the power level to produce an optical signalwith sufficient power to drive a fiber optic cable 204.

According to various embodiments, laser 201 may be implemented using avariety of laser technologies. For example, a diode laser may be astand-alone chip or integrated together with optical components 202, forexample. Low power operation and higher reliability may be particularlyuseful for non-direct modulated lasers, for example. In someembodiments, laser 201 may be a hybrid silicon laser with a III-V gainchip bonded onto a chip with a reflecting mirror made of opticalgratings on silicon waveguides from both sides of the laser, forexample. Other examples may be indirectly modulated electro-absorptionmodulated laser (EML) comprising a laser diode section configured tooperate under a continuous wave (CW) condition and an electro-absorptionmodulation section to generate optical output signals. Yet otherexamples may be continuous wave (CW) lasers modulated by integratedsilicon modulators, for example.

Optical components 202 may include waveguides, splitters, arrayedwaveguide gratings, optical modulators, and/or photodetectors (e.g., fortransceiver applications). In some embodiments, optical components 202may be integrated on the same substrate, such as a semiconductorsubstrate, for example. Integrated silicon optical components are oftenreferred to as “Silicon Photonics.” A Silicon Photonics chip integratedwith one or more diode lasers is an example of an “optical engine.”

In some embodiments described in more detail below, electrical circuitryand optical components may be combined onto a common substrate, such asthe same printed circuit assembly. This is sometimes referred to asco-packaged optics (“CPO”). CPO may reduce input/output (I/O) power bylimiting electrical signaling to intra-package distances. CPO may reducecosts by increasing channel count per optical sub-assembly, by reducingthe power required per bit, and by eliminating discrete transceiverpackaging as well as minimizing the need for high-speed PCB traces. CPOmay further support high-density optical faceplate connectors on anetwork device chassis, for example.

Accordingly, while the electrical data, laser, and optical componentsare illustrated in FIG. 2A as separate blocks, it is to be understoodthe such blocks may reside on one or more substrates or printed circuitassemblies, for example.

As mentioned above, one aspect of the present disclosure pertains tooperating lasers at a low power level corresponding to a higherreliability, and coupling the optical signal through a semiconductoroptical amplifier to increase the power level at the input to theoptical fiber (e.g., to meet link power requirements).

From the equations above, it can be seen that lower power levelsincrease laser reliability. Accordingly, embodiments of the disclosureinclude configuring laser 201 to produce an optical signal with a firstpower level corresponding to a mean time to failure (MTTF) above aparticular target value. SOA 203 is configured to produce the opticalsignal with a second power level configured to drive the optical fiber(e.g., corresponding to a predetermined power link budget), for example.Different laser technologies may be operated at different low powerlevels to achieve higher reliabilities and meet link power budgets aswould be understood by those skilled in the art based on the presentdisclosure. Low power may correspond to a current density of the laser.For instance, low power operation continuous wave lasers modulated byexternal integrated silicon optical modulators may be configured with acurrent density below 4000 A/cm² per optical output channel (e.g., foreach modulator driven by the laser). For example, a ratio betweencurrent density of the one or more continuous wave lasers to the numberof optical channels driven by one laser may be below 4000 A/cm2 perchannel.

The following are further examples of low power operation correspondingto higher reliability for optical communication applications. For a twosection electro-absorption modulated DFB laser (e.g., an EML), theoutput power may be less than 1 mW (Po<1 mW). As another example, ahybrid silicon laser based on a III-V (e.g., InGaAs/InP) gain chipbonded on a silicon waveguide including wavelength selection elementsmay operate with an output power less than 10 mW (Po<10 mW). As yetanother example, a continuous wave (CW) distributed feedback laser (DFB)modulated by external silicon photonic modulator may operate with anoutput power less than 10 mW. Additionally, a multiple-wavelength laser(comb laser or mode-locked laser) based on Quantum Dots (e.g., havingmore than 4 lasing modes) may operate with an output power less than 5mW per channel. A quantum dot laser is a semiconductor laser that usesquantum dots as the active laser medium in its light emitting region.Quantum dots (QDs) are tiny semiconductor particles on the scale ofnanometers in size, having optical and electronic properties that differfrom larger particles due to quantum mechanics. Quantum dots haveproperties intermediate between bulk semiconductors and discrete atomsor molecules. Their optoelectronic properties change as a function ofboth size and shape as is understood by those skilled in the art. Whenreferring to laser power, it is common to refer to the power of a lasermode. For instance, for a continuous wave (CW) distributed feedbacklaser (DFB), laser power is equal to the power of the laser mode. For aquantum dot comb laser, the power of a laser mode is equal to the laserpower divided by the number of modes, for example.

In some embodiments, a ratio of the laser output power divided by theSOA output power is illustrative of low power laser operation. Forexample, for an electro-absorption modulated DFB laser the ratio of thelaser output power to SOA output power may be in the range of 3-20(e.g., less than 20), for example. However, for DFB lasers (e.g., onelasing wavelength per laser) or Quantum Dot (QD) based comb lasers (8,16, 32 etc lasing wavelength per laser), which may be continuouswavelength (CW) lasers configured with Silicon Photonics, for example,the ratio of the laser output power to SOA output power may be in therange of 3-20 (e.g., less than 20), for example. For instance, invarious embodiments, laser output power and SOA output powers may be asillustrated in TABLE 1 below:

TABLE 1 Laser power, mW SOA power, mW Ratio (Laser/SOA) 15 1 15 10 1 105 1 5 3 1 3 1 1 1 30 2 15 20 2 10 10 2 5 5 2 2.5 1 2 0.5 15 0.5 30 100.5 20 5 0.5 10 2.5 0.5 5 1 0.5 2 10 0.25 40 5 0.25 20 2.5 0.25 10 10.25 4

In various embodiments, different lasers may be driven with differentdrive currents. The drive current relates to the output power. The drivecurrent typically is above a threshold current for the laser to operate.Accordingly, for a low power/improved reliability laser according toembodiments herein, the drive current may be maintained close to thethreshold current. For example, in other embodiments the drive currentmay not exceed the threshold current multiplied by 7. In someembodiments, the drive current may not exceed the threshold currentmultiplied by 4, for example.

Traditionally, Data Center computer networks have been considered “shortreach” networks, where SOAs are not typically used. According to someembodiments, one or more lasers may generate optical signals withwavelengths in the O-band (e.g., around 1.3 um (i.e., 1.3 micrometers)).Accordingly, SOAs may amplify one or more wavelengths in the O-band, forexample.

As mentioned above, higher reliability may be obtained by reducing drivecurrent density and thereby laser power and including an SOA. However,adding components to a system, such as SOA 203, typically reducesreliability due to the additional potential failure of the addedcomponents. According to various embodiments, by reducing the power ofthe laser and including an SOA in the channel to drive the fiber, thesystem reliability increases relative to some high power laser systems.For instance, the increase in reliability of one or more lasers in anoptical transmitter may be greater than the reduction in reliabilityfrom an SOA, and thus the system reliability increases. Additionally,even though the SOA may fail, in some embodiments, the SOA may be easilyreplaced by simply replacing the fiber cable with a new fiber and SOA,for example.

For some example embodiments, such as silicon photonics platforms, lowinput power from the laser may decrease the power consumption ofintegrated photonic components. For example, in some example integratedphotonic systems, the majority of light (e.g., >90%) may be scatteredinside of the silicon chip. Accordingly, lower absolute input power mayimprove the system performance due to lower potential crosstalk issues(e.g. on photodetectors on a receiver part) induced by the light, forexample.

Additionally, the contribution to power consumption from an SOA moduleor chip(s) may be relatively small because the output power of an SOAmay be substantially lower than a higher powered laser (e.g., 30mW×8=240 mW for 8 CW DFB lasers used for 800G transceivers). FIG. 2Billustrates a comparison of power consumption for an example laser. Oneexample current drive circuit is illustrated at 250, including anoperational amplifier 251, NPN transistor 252, and resistors R2-R5coupled to a continuous wave (CW) laser 253. Table 260 illustratessystem power consumption for a high-powered laser without an SOA and alow powered laser with an SOA. As illustrated in table 260, the totalpower in this example is reduced from about 340 mW per channel to about50 mW per channel, which in a networking application is a reduction inpower of about 0.3 W per 100G or 2.3 W for 800G, for example.Accordingly, reducing the laser power may further reduce overall systempower consumption.

In some embodiments, various formats of light modulation in the opticallink of the present disclosure may be used, both for pluggabletransceivers and co-packaged optics. The modulation formats includeNon-Return-to-Zero (NRZ), Pulse-Amplitude Modulation (PAM) andQuadrature Amplitude Modulation (QAM) with coherent detection, forexample.

Reducing the laser power may also be beneficial from an eye-safety pointof view. For example, in the case of continuous wave (CW) lasers, whichmay pump a Silicon Photonics chip (e.g., inside a network switch), theymay be operated at significantly lower power levels. Such lasers, aswell as the pluggable modules including such lasers as described infurther examples below, can meet Class 1 or 1M eye safety standards. Thesignal amplification needed to boost the power to the level required bythe optical link power budget can be done via SOA chip(s) or module(s),for example.

Yet further, low power lasers move a portion of power consumption, heat,and cost of optics integrated with electronics toward the fiber output(e.g., from inside a network switch internally toward a faceplate asdescribed in more detail below). Advantageously, lower heat load mayalso improve laser reliability.

As described in more detail below, features and advantages of thepresent disclosure may further include an SOA, which may be pluggable toor configured on a module with other optical components of atransceiver. As illustrated in FIG. 2A by the dashed lines, in thisexample embodiment SOA 203 may be selectively connected and disconnectedfrom optical components 202 (e.g., plugged and unplugged by a user). SOA203 may be permanently fixed to the fiber optic cable 204. Accordingly,when an SOA fails, it may be easily replaced by simply unplugging thecable connector, for example. In another embodiment, the SOA andintegrated silicon optical components may be integrated on a singlemodule. For example, a SOA chip may be integrated on a module that isalso configured with other optical components, such as integratedsilicon optical components, lasers, or both. In some embodiments, an SOAchip may be integrated on top of (e.g., bonded on) an integrated siliconoptical components chip, for example, after a modulator in theintegrated silicon optical components chip. These integrated modules maybe inside a transceiver or chassis (as described further below) and maynot be pluggable.

FIGS. 3A-B illustrate optical transmitters with pluggable SOAs accordingto various embodiments. Transmitter 300A may be a portion of atransceiver as described further below, for example. Referring to FIG.3A, a plurality of lasers 301A-301N may each generate different opticalwavelengths. The optical wavelengths are coupled to integrated siliconoptical components 303 (Silicon Photonics), which may includemultiplexers for combining the different wavelengths and modulators formodulating the wavelengths based on electrically encoded data to betransmitted, for example. In this example, an optical signal comprisinga plurality of modulated wavelengths is output from integrated opticalcomponents 303 on an integrated waveguide 304. Integrated waveguide 304may be a planar waveguide (PWG). In various embodiments, siliconwaveguides in an integrated optical components chip may be coupled topolymer-based optical waveguides on a printed circuit board or fiberoptic cables (e.g., for single mode or multimode depending on thespecification of the links). In one embodiment, the waveguides may bepolarization maintaining (PM) to meet polarization requirements of theoptical link, for example. In FIG. 3A, the integrated optical components303 are coupled to SOA 310 using polymer-based optical waveguides 304and 309, which may be on printed circuit boards, for example. Awaveguide-to-waveguide connector (WG-WG conn.) 305 may be configured toengage two printed circuit boards, for example. Connector 305 includesone or more coupling waveguides 306 to optically couple waveguides 304and 309 to establish an optical link from lasers 301A-301N to an inputof SOA 310, for example. An output of SOA 310 is coupled to a waveguide311, which in turn is coupled to a fiber optic cable 312. Fiber opticcable 312 may be fixedly attached to a module 307 comprising SOA 310 andwaveguides 309 and 311. Module 307 is configured to connect to WG-WGconnector 305 so that the SOA and fiber are pluggable (e.g., into asocket 308), for example.

FIG. 3B illustrates another example optical transmitter 300B withpluggable SOA according to various embodiments. In this example, anoutput of integrated optical components 300B is coupled together usingfiber optic cables. For example, fiber optic cable 320 is coupled to oneinput of a fiber-to-fiber connector 321, which engages two printedcircuit boards, for example. Connector 321 includes one or more couplingwaveguides 322 to optically couple fibers 320 and 325 to establish anoptical link from lasers 301A-301N to an input of SOA 326, for example.An output of SOA 326 is coupled to fiber optic cable 328. Fiber opticcable 328 may be fixedly attached to a module 323 (comprising SOA 326and fibers 325 and 327) and configured to connect to fiber-to-fiberconnector 321 so the SOA and fiber are pluggable (e.g., into a socket324), for example.

While connectors 305 and 321 are shown here as connecting one pair ofwaveguides, it is to be understood that optical connectors 305 and 321may connect multiple pairs of waveguides in various embodiments.Additionally, while FIG. 3A illustrates coupling optical componentstogether using integrated waveguides and FIG. 3B illustrates couplingoptical components together using fiber optic cables, variouscombinations of these approaches may also be used.

Optical transmitters and transceivers according to various embodimentsmay be used in a variety of applications. For example, one applicationof the concepts described herein is computer networking, such as in aData Center. Data Center network topologies are typically characterizedby the use of multiple layers of switches. Different layers of topologyare typically called core, spine, and leaf. Switches on the lowest levelare connected to the server or server rack. Embodiments of the presentdisclosure may be applicable for the switches of all topology levels, aswell as to the servers, racks of several servers, or other networkdevices, for example.

Switches for large scale Data Centers and Enterprise Data Centerstypically include data switching and routing managed by specialintegrated circuit (e.g., ASIC) chipsets. Traditionally, network trafficis delivered via printed-circuit board copper traces to the front panelto connectors for pluggable optical transceivers. Optical signals aredelivered by optical fiber to another switch or rack unit with multipleservers. For very short distances coaxial electrical cables are also inuse. The switches used in Data Centers today have faceplate-mountedpluggable optical transceiver modules. The signals from the ASICs(switch chipset, CPU, etc.) are delivered to transceivers by PCBinterconnect traces.

Embodiments of the present disclosure may improve computer networks. Insome embodiments, electrical I/O which drives the optical engines areshorter in length and can be optimized for intra-package reach whileconsuming low power. Advantageously, high-speed I/O may be transportedon and off the package on optical fibers attached to the photonicscomponents.

FIG. 4 illustrates a network device including a pluggable SOA moduleaccording to an embodiment. In various embodiments, a network device mayinclude a chassis 400, optics modules comprising lasers 410A-Nconfigured to produce an optical signal, an integrated opticalcomponents unit 412 configured to receive the optical signal from thelasers 410A, semiconductor optical amplifiers (SOA) 425 configured toreceive the optical signal from the integrated optical components unit412, and an optical fiber 450 coupled to an output of an SOA 425, forexample. As described above, the lasers are operable at a low powerlevel corresponding to a higher reliability and one or more SOAs 425increase the power level at the input to the optical fiber 450.

In this example, SOA 425 is configured on a pluggable printed circuitassembly (PCA) module. Chassis 400 may include a plurality of sockets,such as pluggable socket 453. Accordingly, SOA 425 is pluggable into oneor more of the plurality of sockets to optically couple and decouplelight signals, for example. The present example shows one pluggable SOA,but it is to be understood that multiple pluggable SOAs may be used.

This example also illustrates an optical transceiver. For instance,network device chassis 400 may include lasers 410A-N, integrated optics412, and pluggable SOA 425 for transmission on fiber 450. Additionally,a receive path may include fiber 451 coupled to a waveguide 426, whichis coupled to an input of integrated optics 412 through a WG-WGconnector 423, for example. Accordingly, for a transceiver application,integrated optics 412 may include integrated waveguides 413, opticalmodulators/demodulators 414, optical multiplexers/demultiplexers 415,and one or more photodetectors 416.

In this example, integrated optics are configured on a PCA 401, and SOA425 is configured on PCA 402. Accordingly, pluggability may be achievedusing planar optical connectors 420 and 423, for example. Fiber opticlines 450 and 451 may be coupled to integrated waveguides on pluggableSOA module 402 using fiber-to-waveguide connectors 421 and 424, whichmay be fixed (non-pluggable). Integrated waveguides on PCA 402 may becoupled to integrated waveguides on PCA 401 using planar opticalconnectors 420 and 423, for example. In this example, some networkdevice electronics 411, such as data switching and control hardware maybe on the same PCA or on a different PCA.

Optical connectors according to various embodiments may includeconnectors mechanically configured to mate waveguides (e.g., on twodifferent PCBs) with low optical loss of light travelling betweenwaveguides (e.g., lower than 3 dB). Optical connectors may have highcoupling efficiency over numerous mate/demate cycles and ambienttemperature fluctuations for life-time of the system. The alignmentbetween planar waveguides on PCBs and optical fiber is known to thoseskilled in the art, and various technologies may be used. For example,one approach may use silicon-based fixtures with V-groves andferrule-sleeve-ferrule interfaces, providing coupling loss on a level of1 dB. Similar technologies can be used for the coupling between planarwaveguides embedded to different PCBs, for example. An optical connectormay also provide protection from dust deposition on its optical element,for example, and may be in a form factor of an MPO connector forexample.

FIG. 5 illustrates an example of a co-packaged module 501 coupled topluggable SOAs according to another embodiment. Here, a network devicechassis 500 includes integrated circuits configured to switch data 511,lasers 510A-N, integrated optical components 512 co-packaged as a singlemodule 501. Co-packaged optics refers to the coupling of optics withintegrated circuits (e.g., an application specific integrated circuit,ASIC) in one package. Co-packaged optics module 501 is coupled to aplurality of pluggable SOAs 502A-N residing in chassis sockets 553A-N,which are in turn coupled to fibers 550A-N, for example. The lasers510A-N, integrated optics 512, and pluggable SOAs 502A-N may beconfigured to transmit one or more wavelengths, including course wavedivision multiplexed wavelengths (CWDM) or dense wave divisionmultiplexed wavelengths (DWDM), for example. In this example, a portionof the network device electronics 511 is included on the co-packagedmodule 501 (e.g., an integrated circuit or ASIC for performing dataplane switching functions). Other network device electronics 590 may beconfigured on other PCBs inside the chassis, for example, such asintegrated circuit for performing control plane functionality (e.g., aCPU), for example.

FIG. 6 illustrates an example of multiple pluggable modules according toanother embodiment. In some embodiments, a plurality of SOAs (e.g., SOAs620A-N) are in first pluggable modules and the lasers and integratedoptics may be in one or more second pluggable modules, for example. Inthis example, network device chassis 600 includes sockets 603A-Nconfigured to receive pluggable modules 621A-N each comprising aplurality of SOAs coupled to fibers 650A-650N. In one embodiment, allSOAs may be configured on one pluggable module. Further, lasers 610A-Nand integrated optics 611 may be configured on a pluggable module 602for easy replacement. In some embodiments, electronics 601 (e.g., a dataplane ASIC for data packet switching and routing) may be included onpluggable module 602.

FIG. 7 illustrates a network device with an integrated optics moduleaccording to an embodiment. In this example, one or more lasers 710A-N,at least one integrated optical components unit 711 (e.g., a siliconphotonics chip) coupled to optical fibers 750, 751 by connectors 718,719, and at least one semiconductor optical amplifier 717 are configuredon a common substrate 702. The resulting module may or may not bepluggable in various embodiments. Module 702 and network deviceelectronics 701 may be configured in network device chassis 700. Module702 may send and receive electrical control and data signals forgenerating and receiving optical signals with very high data rates, forexample.

FIG. 8 illustrates a network device with pluggable optics according toanother embodiment. In some embodiments, the optical channels also canbe routed such that Tx channels go through the SOA module (a singlechannel per SOA, or multiple channels per SOA), whereas Rx signals tothe network device are delivered by different optical fibers using alow-cost pluggable optical connector to pass the light into embeddedwaveguides on a device PCA, for example. In this example, a networkdevice comprises a chassis 800, including one or more PCAs 801 includingelectrical and optical components 802. Pluggable SOAs 810A-N areconfigured to send optical signals (e.g., single wavelength or multiplewavelengths). In this example, the network device further comprises apluggable optical coupler module 820 configured to receive an opticalsignal and couple the optical signal to at least one integrated opticalcomponents unit in the electrical/optical components 802. Accordingly,SOA transmitters, which may experience higher failure rates, may beeasily replaced separately from optical receive channel components,which may have lower failure rates, for example.

FIG. 9 illustrates an example configuration of printed circuit modulesaccording to an embodiment. In some embodiments, a network device mayinclude one or more planar optical connectors configured to opticallycouple a first polymer waveguide on a first printed circuit assemblycomprising the at least one integrated optical components module and asecond polymer waveguide on a second printed circuit assembly comprisingthe at least one semiconductor optical amplifier. In this example, anetwork device includes a chassis (not shown), single or multiple PCAs901-902, optical connectors 910-912 for passive optical alignment(optical couplers) in order to couple light between a planar waveguides(PWG) (e.g., WG 920 and WG 926) on SOA PCA 901 and PCAs 902, forexample. Optical connectors 910 and 911 provide optical connections withthe fibers 950 and 951, respectively. Waveguides on both PCAs may have atapered beam expansion section (e.g., 924/925) to convert an opticalmode of an optical signal. The expanded section may be configured largeenough so that passive optical alignment can be used with low couplingloss. It is to be understood that other passive light couplingtechniques can be used, including evanescent field light coupling, forexample. PCA 901 has an SOA chip 921, which may be based on eitherInGaAsAl/InP Quantum Wells or InGaAs/AlGaAs Quantum Dots, for example.Both facets of the SOA chip may have Anti-Reflection Coating (AR). Thewaveguide coupled to the SOA chip might have a curved design on bothsides of the chip making light reflection on the chip facets take placeunder an angle to enhance anti-reflection. In some example embodiments,the length of the SOA chip 921 may vary from 0.5 to 8 mm. SOA chip 921may receive drive current from a direct current (DC) driver 922, forexample. The SOA chip 921 may be single mode to support a single modelink, which may be used for longer reaches, or can be multimode forshorter reach multimode transmission, for example. On the receiver (Rx)line, the light travels from external fiber 951 through a polymer-basedwaveguide to the optical connector 912 and later to a polymer waveguideon PCA 901. A laser driver IC and all required passive and activecomponents may be placed on the same PCB as described above, forexample. In this example, a set of filtering capacitors 923 may be usedto reduce the drive current noise (e.g., based on the overall linkrequirements). Thermoelectric coolers (TEC) can be placed inside ofthose SOA modules with high output power, whereas for moderate powerlevels an uncooled operation of SOA chip 921 may be used. A mountingscheme where all or several SOA modules are coupled to an externalpassive or active heatsink is also possible.

FIGS. 10 and 11 illustrate example configurations of printed circuitmodules according to alternative embodiments. In FIG. 10 , an SOA chip1001 is configured in the receive path. In FIG. 11 , SOA chips 1101 and1102 are configured in the receive and transmit paths, respectively.

FIG. 12 illustrates an example power link budget estimate according toan embodiment. In this example, DFB lasers are configured in a CPOmodule and driven at low output power in a 51.2 Tbps datacenter switchwith 32 ports. Each port may have a bandwidth of 1.6 Tbps aggregatedfrom 16×100 Gbps PAM4 channels. A single quantum dot (QD) SOA chipoperates in a regime close to gain saturation (e.g., low differentialgain) and amplifies all 16 lasing modes simultaneously withoutgeneration of additional mode partition noise as described above. Thewavelengths are modulated using 16 Mach-Zahnder modulators (describedfurther below), multiplexed onto a single waveguide, amplified andtransmitted. Another receiver demultiplexes the wavelengths, which arethen sensed by photodetectors. Losses from polymer-based waveguidesembedded on the switch PCA and SOA PCA may be 0.05 dB/cm, for example,and are not taken into account. The coupling losses in this example areat a level of 1 dB for PWG-to-fiber and PWG-to-SOA chip coupling and 2dB for PWG-to-PWG coupling. Typically, a continuous wave (CW) DFB laseroutput power may be as high as 25 mW due to significant total insertionloss of the silicon photonics chip. Thus, the laser drive currentdensity is well above the threshold current density. However, accordingto the present example embodiment, one can drive the laser at 10 timeslower drive current, for example, because the optical signal isamplified in an SOA module pluggable to the switch. Reductions in drivecurrent may be similarly applicable for QD Comb Lasers (e.g., withSilicon Micro-ring Resonators acting as modulators) and EML lasers, forexample.

FIG. 13 illustrates an example network device including opticaltransceivers according to an embodiment. In this example, a networkswitch comprises a PCA 1301 including a comb laser 1310 generating 16wavelengths (e.g., Fabry-Pérot (FP) modes).

A comb laser (or frequency comb-based laser) is a light source with aspectrum consisting of frequency equidistant lines, each correspondingto one longitudinal cavity mode. For example, comb laser 1310 may be amonolithic comb-laser diode chip is based on InAs/InGaAs quantum dots inGaAs/AlGaAs materials system.

Accordingly, multiple wavelengths may be generated and modulated by asilicon photonics chip 1311. In this example, silicon photonics chip1311 includes ring modulators 1312. Ring modulators are a type ofoptical ring resonator, which comprise a set of waveguides in which atleast one is a closed loop coupled to some sort of light input andoutput. When light of the resonant wavelength is passed through the loopfrom an input waveguide, it builds up in intensity over multipleround-trips due to constructive interference and is output to the outputbus waveguide which serves as a detector waveguide. Light in the ringmay be modulated by electrically altering the optical properties of thering, such as a coupling coefficient.

The output wavelengths of the modulator are coupled to a quantum dot SOAchip 1313 on a pluggable module 1302, amplified, and transmitted over afiber. Another switch may include a pluggable module 1303 comprising anSOA chip 1314 for amplifying the received wavelengths. A switch PCA 1304includes a photonics chip 1315 comprising a demultiplexer 1316 (whichmay also be ring based) and 16 phase detectors 1317(1)-1317(16). In thepresent example, because additional lasing lines are coming at no costfor comb lasers and multiple lines can be amplified by a single SOA chipbased on QDs, certain embodiments may advantageously use more linesmodulated at lower speed, because the cost and power consumption ofdriving electronics is higher for higher speed. For example, 16 lasingmodes modulated at 100G PAM4 (25G) to get 1.6 Tbps aggregated data ratemay be used in some embodiments.

FIG. 14 illustrates another example network device with pluggableoptical components according to an embodiment. As mentioned above, oneor more SOAs may be pluggable. In this example, all the SOA chips areconfigured on one module. Here, a CPO module on a network switch PCA1401 includes a plurality of silicon photonics engines (e.g., lasers andintegrated optical components; electronics not shown), such as engine1402, which may include 16 CW DFB lasers or a single comb laser, forexample. A single pluggable SOA module 1403 may include a plurality ofSOAs, such as SOA 1404, for example. Each optical input and output pathmay be coupled to a fiber using a fiber connector, such as fiberconnector 1405, for example. More specifically, in one embodiment, a51.2 Tbps switch may include 32 optical engines based on a SiliconPhotonics platform using 1.6 Tbps bandwidth. In another embodiment, 16light engines at 3.2 Tbps data rate each may be used. Such an integratedmodule may previously suffer from the reliability issues describedabove, because it contains many photonics components with high opticalpower and current density. However, low powered lasers shift reliabilityissues to the SOAs, which may be replaced in case of failure withoutdismounting the switch, for example. Because there is no high-speedelectronics inside of the SOA module, it's cost may not be as high.Alternatively, other embodiments may have 2, 4, 8 etc. independent SOAmodules to amplify different numbers of lasing lines, for example. Thetechniques described herein may be used to estimate the number of SOAchips/pluggable modules based on drive conditions, number of lasinglines amplified, and specific requirements of a particular networkdevice, for example, in order to get the best combination of cost,performance, and MTBF level.

FIG. 15 illustrates another configuration of lasers and semiconductoroptical amplifiers according to another embodiment. In this example, anetwork switch PCA 1501 comprises an electronic data plane ASIC 1502 anda Silicon Photonics chip 1503 (e.g., with integrated optical componentsdescribed above) with pluggable modules for both low power CW lasers1504 and SOAs 1505, which may be placed on a path to the receiver of asecond network switch, for example. ASIC 1502 and Silicon Photonics chip1503 may be co-packaged optics, for example. The present exampleillustrates that another way to mitigate laser reliability issues innetwork devices is to place lasers to place the lasers in pluggableoptical modules located on the panel (e.g., rather than inside theswitch chassis close to the Silicon Photonics light engine). The CWlight from these lasers is delivered by optical fiber or by planarwaveguides (e.g., over the network device PCA) to the Silicon Photonicschip(s) placed next to the switch ASIC, modulated, and sent to pluggableSOA 1505, for example, and then to another network device.

In some embodiments, the SOA chip or multiple SOA chips may beconfigured on the same pluggable module as the lasers, for example. Inthis case, the resultant module has multiple functions: contain lowpower laser(s) which pump a Silicon Photonics engine, amplification ofthe optical signal after it has been modulated by the Silicon Photonicschip inside of the network device, and delivery of the signal to theoptical fiber connected to a receiver of a second network device. Thesignal from a transmitter of the second network device to the receiverof the first network may also be channeled through the same pluggablemodule (e.g., on a second receiver path fiber). For example, the signalarrives through the optical fiber and is moved into polymer waveguidescontained on the PCA of the pluggable module, for example.

FIGS. 16A-B illustrate another network device with pluggable opticsaccording to an embodiment. In FIG. 16A, a network switch printedcircuit assembly 1601 is coupled to a pluggable module 1602 comprisingboth an SOA 1613 and CW laser 1610. Laser 1610 on pluggable module 1602generates one or more wavelengths of light, which are received by asilicon photonics chip 1611 as mentioned above. Chip 1611 may be coupledto switch electronics 1612, which may be an ASIC. Modulated wavelengthsmay be transmitted back to module 1602 and to the input of SOA chip1613. SOA chip 1613 has an output coupled to a fiber 1614 fortransmitting (Tx) modulated optical signals to another network device.As illustrated in FIG. 16B, pluggable module 1602 may further include areceive (Rx) path via fiber 1615, as described above, for couplingreceived optical signals from another network device to a photodetectorin silicon photonics chip 1611, for example.

FURTHER EXAMPLES

In various embodiments, the present disclosure includes systems,methods, and apparatuses for optical communications.

In one embodiment, the present disclosure includes an opticaltransceiver comprising: one or more continuous wave lasers configured toproduce an optical signal; at least one integrated silicon opticalcomponents unit comprising at least one modulator configured to receivethe optical signal from the one or more lasers; at least onesemiconductor optical amplifier configured to receive the optical signalfrom the at least one optical components unit; and an optical fibercoupled to an output of the at least one semiconductor opticalamplifier, wherein the one or more lasers are operable at a low powerlevel corresponding to a first reliability above a target threshold, andwherein the at least one semiconductor optical amplifier increases thepower level of the optical signal on its way to the optical fiber.

In one embodiment, the optical signal wavelength from the one or morelasers is around 1.3 um.

In one embodiment, the one or more continuous wave lasers include acontinuous wave distributed feedback laser.

In one embodiment, the one or more continuous wave lasers include aquantum dot comb laser generating a plurality of wavelengths.

In one embodiment, the low power level is insufficient to transmit theoptical signal through a full length of the optical fiber and theoptical amplifier increased power is sufficient to transmit the opticalsignal through the full length of the optical fiber.

In one embodiment, the low power level corresponds to a mean time tofailure above a first value, and wherein the semiconductor opticalamplifier is configured to produce the optical signal with a secondpower level coupled to the optical fiber.

In one embodiment, a current density of the one or more continuous wavelasers is below 4000 A/cm² per optical output channel.

In one embodiment, at least one of said lasers is a hybrid silicon laserbased on a III-V gain chip bonded on a silicon waveguide includingwavelength selection elements and the power is less than 10 mW.

In one embodiment, at least one of said lasers is a continuous wavedistributed feedback laser and the power is less than 10 mW.

In one embodiment, at least one of said lasers is a quantum dot comblaser and the power is less than 5 mW per channel.

In one embodiment, the one or more lasers comprise a drive current, andwherein the drive current does not exceed a threshold current multipliedby 7.

In one embodiment, at least one of said lasers is a continuous wavedistributed feedback laser, and wherein a ratio of a laser output powerto a semiconductor optical amplifier output power per channel is lessthan 20.

In one embodiment, at least one of said lasers is a continuous wavequantum dot comb laser, and wherein a ratio of a laser output power to asemiconductor optical amplifier output power per channel is less than20.

In one embodiment, at least one of said lasers is a continuous wavequantum dot comb laser producing a plurality of wavelengths, and whereinthe plurality of lasers are coupled to a single quantum dotsemiconductor optical amplifier to amplify a plurality of wavelengths.

In one embodiment, a plurality of the continuous wave lasers eachproduce a single wavelength, and wherein the plurality of continuouswave lasers are coupled to a single quantum dot semiconductor opticalamplifier to amplify a plurality of wavelengths.

In one embodiment, the laser is coupled to the semiconductor opticalamplifier over an optical polarization maintaining waveguide.

In one embodiment, the semiconductor optical amplifier operates in again saturation regime.

In one embodiment, the optical transceiver further comprises an opticalconnector configured between the at least one optical components unitand the at least one semiconductor optical amplifier, wherein thesemiconductor optical amplifier is pluggable.

In one embodiment, the at least one optical components unit, the opticalconnector, and the at least one semiconductor optical amplifier arecoupled together using one or more fiber optic cables.

In one embodiment, the at least one optical components unit, the opticalconnector, and the at least one semiconductor optical amplifier arecoupled together using one or more integrated optical waveguides.

In one embodiment, the at least one optical components unit isconfigured on a first planar printed circuit assembly and the at leastone semiconductor optical amplifier is configured on a second planarprinted circuit assembly, and wherein the optical connector is a planaroptical connector.

In one embodiment, the at least one integrated silicon opticalcomponents unit and the at least one semiconductor optical amplifier areconfigured on a single module.

In one embodiment, the at least one semiconductor optical amplifier isbonded on top of the at least one integrated silicon optical componentsunit after one or more modulators in the at least one integrated siliconoptical components unit.

In one embodiment, the at least one modulator is a micro-ring modulator.

In one embodiment, the at least one modulator is a Mach-Zehndermodulator.

In one embodiment, the at least one modulator is an electro-absorptionmodulator.

In one embodiment, the optical signal is pulse-amplitude modulated.

In one embodiment, the optical signal is quadrature amplitude modulated.

In another embodiment, the present disclosure includes an opticaltransceiver comprising: one or more electro-absorption modulateddistributed feedback lasers configured to produce an optical signal, theone or more lasers comprising: a laser diode section configured tooperate under a continuous wave (CW) condition; and anelectro-absorption modulation section to generate an optical outputsignal; at least one semiconductor optical amplifier configured toreceive the optical signal from at least one of the electro-absorptionmodulated distributed feedback lasers; and an optical fiber coupled toan output of the at least one semiconductor optical amplifier, whereinthe one or more lasers are operable at a low power level correspondingto a first reliability above a threshold, and wherein the at least onesemiconductor optical amplifier increases the power level of the opticalsignal on its way to the optical fiber.

In one embodiment, the optical signal from the one or more lasers isaround 1.3 um.

In one embodiment, a current density of the one or moreelectro-absorption modulated distributed feedback lasers is below 7000A/cm².

In one embodiment, the output power is less than 1 mW.

In one embodiment, a ratio of a laser output power to a semiconductoroptical amplifier output power is less than 20.

In one embodiment, the laser is coupled to the semiconductor opticalamplifier over an optical polarization maintaining waveguide.

In one embodiment, one or more electro-absorption modulated distributedfeedback lasers are coupled to a single quantum dot semiconductoroptical amplifier to amplify a plurality of wavelengths.

In one embodiment, the one or more electro-absorption modulateddistributed feedback lasers are configured on a first planar printedcircuit assembly and the at least one semiconductor optical amplifier isconfigured on a second planar printed circuit assembly, and wherein theoptical connector is a planar optical connector.

In one embodiment, the semiconductor optical amplifier is pluggable, theoptical transceiver further comprises an optical connector configuredbetween the at least one optical components unit and the at least onesemiconductor optical amplifier.

In another embodiment, the present disclosure includes a network devicecomprising: a chassis; one or more lasers configured to produce anoptical signal; at least one integrated silicon optical components unitconfigured to receive the optical signal from the one or more lasers; atleast one semiconductor optical amplifier configured to receive theoptical signal from the at least one optical components unit; and anoptical fiber coupled to an output of the at least one semiconductoroptical amplifier, wherein the one or more lasers are operable at a lowpower level corresponding to a higher reliability, and wherein the atleast one semiconductor optical amplifier increases a power level of theoptical signal on its way to the optical fiber.

In one embodiment, the optical signal from the one or more lasers isaround 1.3 um.

In one embodiment, the one or more lasers are configured to produceoptical signals with a first power level corresponding to a mean time tofailure above a first value, and wherein the at least one semiconductoroptical amplifier is configured to produce the optical signal with asecond power level configured to drive the optical fiber.

In one embodiment, the one or more lasers comprise a drive current, andthe drive current does not exceed a threshold current multiplied by 7.

In one embodiment, the network device further comprises a plurality ofsockets on the chassis, wherein the at least one semiconductor opticalamplifier is pluggable into one or more of the plurality of sockets.

In one embodiment, the network device further comprises one or moreintegrated circuits configured to switch data, wherein a plurality ofthe semiconductor optical amplifiers are pluggable into the plurality ofsockets, and wherein the one or more integrated circuits, the one ormore lasers, and the at least one optical components unit areco-packaged in a single module.

In one embodiment, the network device further comprises a plurality ofoptical connectors configured in at least a portion of the plurality ofsockets, each optical connector optically coupling at least one opticalcomponents unit to at least one semiconductor optical amplifier.

In one embodiment, a plurality of semiconductor optical amplifiers areconfigured on at least one first pluggable module configured to pluginto one the plurality of sockets, and wherein the one or more lasersare configured on at least one second pluggable module.

In one embodiment, the at least one second pluggable module isconfigured to plug into one of the plurality of sockets.

In one embodiment, the at least one semiconductor optical amplifier andthe at least one laser are configured on a first pluggable moduleconfigured to plug into one of the plurality of sockets.

In one embodiment, the one or more lasers, the at least one opticalcomponents unit, and the at least one semiconductor optical amplifierare configured on a common substrate.

In one embodiment, the network device further comprises a pluggableoptical connector configured to receive an optical signal and couple theoptical signal to the at least one optical components unit.

In one embodiment, the network device further comprises a planar opticalconnector configured to optically couple a first polymer waveguide on afirst printed circuit assembly comprising the at least one opticalcomponents unit and a second polymer waveguide on a second printedcircuit assembly comprising the at least one semiconductor opticalamplifier.

In one embodiment, the first polymer waveguide and the second polymerwaveguide are tapered to convert an optical mode of an optical signal.

In one embodiment, the optical signal is pulse-amplitude modulated.

In one embodiment, the optical signal is quadrature amplitude modulated.

In another embodiment, the present disclosure includes a network devicecomprising: a chassis comprising a plurality of sockets; one or morelasers configured to produce an optical signal; at least one integratedsilicon optical components unit configured to receive the optical signalfrom the one or more lasers; and one or more optical connectorsconfigured proximate to one or more of the plurality of sockets, whereinthe optical connectors are coupled to the at least one integratedsilicon optical components unit and are configured to couple to at leastone pluggable semiconductor optical amplifier to receive the opticalsignal from the at least one integrated silicon optical components unitand produce an amplified optical signal to an optical fiber coupled toan output of the at least one semiconductor optical amplifier.

In one embodiment, the at least one integrated silicon opticalcomponents unit is configured on a first printed circuit assembly andthe semiconductor optical amplifier is configured on a second printedcircuit assembly, and wherein the optical connector is a planar opticalconnector.

In one embodiment, the at least one integrated silicon opticalcomponents unit, the optical connector, and the at least onesemiconductor optical amplifier are coupled together using one or moreintegrated optical waveguides.

In one embodiment, the network device further comprises at least oneintegrated circuit for switching data, wherein the one or more lasers,the at least one integrated silicon optical components unit, and theintegrated circuit for switching data are co-packaged.

In another embodiment, the present disclosure includes a method forsending data across a network comprising: generating an optical signalin one or more continuous wave lasers, wherein the one or morecontinuous wave lasers are operable at a low power level correspondingto a target reliability; coupling the optical signal to at least oneintegrated silicon optical components unit; and coupling the opticalsignal from the at least one integrated silicon optical components unitto at least one semiconductor optical amplifier; and coupling theoptical signal from an output of the at least one semiconductor opticalamplifier to an optical fiber, wherein the at least one semiconductoroptical amplifier increases a power level of the optical signal of theoptical signal on its way to the optical fiber.

In another embodiment, the present disclosure includes a method ofsending data across a network comprising: generating an optical signalin one or more lasers; coupling the optical signal to at least oneintegrated silicon optical components unit; and coupling the opticalsignal from the at least one integrated silicon optical components unitto at least one optical connector configured proximate to at least onesocket of a network device chassis, wherein the at least one opticalconnector is configured to couple to a pluggable semiconductor opticalamplifier to receive the optical signal from the at least one integratedsilicon optical components unit through the optical connector andproduce an amplified optical signal to an optical fiber coupled to anoutput of the at least one semiconductor optical amplifier.

The above description illustrates various embodiments along withexamples of how aspects of some embodiments may be implemented. Theabove examples and embodiments should not be deemed to be the onlyembodiments, and are presented to illustrate the flexibility andadvantages of some embodiments as defined by the following claims. Basedon the above disclosure and the following claims, other arrangements,embodiments, implementations and equivalents may be employed withoutdeparting from the scope hereof as defined by the claims.

What is claimed is:
 1. A network device comprising: a chassis; one ormore lasers configured to produce an optical signal along a transmissionpath toward an optical fiber; at least one integrated silicon opticalcomponents unit in the transmission path configured to receive theoptical signal from the one or more lasers; and at least one quantum dotsemiconductor optical amplifier in the transmission path configured toreceive the optical signal from the at least one optical componentsunit; wherein the optical fiber is coupled to an output of the at leastone semiconductor optical amplifier, and wherein the one or more lasersare operable below 10 mW per channel.
 2. The network device of claim 1wherein the optical signal from the one or more lasers is around 1.3 um.3. The network device of claim 1 wherein the one or more lasers areconfigured to produce optical signals with a first power levelcorresponding to a mean time to failure above a first value, and whereinthe at least one quantum dot semiconductor optical amplifier isconfigured to produce the optical signal with a second power levelconfigured to drive the optical fiber.
 4. The network device of claim 1wherein the one or more lasers comprise a drive current, and the drivecurrent does not exceed a threshold current multiplied by
 7. 5. Thenetwork device of claim 1 further comprising a plurality of sockets onthe chassis, wherein the at least one quantum dot semiconductor opticalamplifier is pluggable into one or more of the plurality of sockets. 6.The network device of claim 5 further comprising: one or more integratedcircuits configured to switch data, wherein a plurality of the quantumdot semiconductor optical amplifiers are pluggable into the plurality ofsockets, and wherein the one or more integrated circuits, the one ormore lasers, and the at least one optical components unit areco-packaged in a single module.
 7. The network device of claim 5 furthercomprising a plurality of optical connectors configured in at least aportion of the plurality of sockets, each optical connector opticallycoupling at least one optical components unit to at least one pluggablequantum dot semiconductor optical amplifier.
 8. The network device ofclaim 5 wherein a plurality of quantum dot semiconductor opticalamplifiers are configured on at least one first pluggable moduleconfigured to plug into one the plurality of sockets, and wherein theone or more lasers are configured on at least one second pluggablemodule.
 9. The network device of claim 8 wherein the at least one secondpluggable module is configured to plug into one of the plurality ofsockets.
 10. The network device of claim 5 wherein the at least onequantum dot semiconductor optical amplifier and the at least one laserare configured on a first pluggable module configured to plug into oneof the plurality of sockets.
 11. The network device of claim 5 whereinthe one or more lasers, the at least one optical components unit, andthe at least one quantum dot semiconductor optical amplifier areconfigured on a common substrate.
 12. The network device of claim 5further comprising a pluggable optical connector configured to receivean optical signal and couple the optical signal to the at least oneoptical components unit.
 13. The network device of claim 1 furthercomprising a planar optical connector configured to optically couple afirst polymer waveguide on a first printed circuit assembly comprisingthe at least one optical components unit and a second polymer waveguideon a second printed circuit assembly comprising the at least one quantumdot semiconductor optical amplifier.
 14. The network device of claim 13wherein the first polymer waveguide and the second polymer waveguide aretapered to convert an optical mode of an optical signal.
 15. The networkdevice of claim 1 wherein the optical signal is pulse-amplitudemodulated.
 16. The network device of claim 1 wherein the optical signalis quadrature amplitude modulated.
 17. A network device comprising: achassis comprising a plurality of sockets; one or more lasers configuredto produce an optical signal along a transmission path; at least oneintegrated silicon optical components unit in the transmission pathconfigured to receive the optical signal from the one or more lasers;and one or more optical connectors configured proximate to one or moreof the plurality of sockets, wherein the optical connectors are coupledto the at least one integrated silicon optical components unit and areconfigured to couple to at least one pluggable quantum dot semiconductoroptical amplifier to receive the optical signal from the at least oneintegrated silicon optical components unit and produce an amplifiedoptical signal to an optical fiber coupled to an output of the at leastone quantum dot semiconductor optical amplifier, wherein the one or morelasers are operable below 10 mW per channel.
 18. The network device ofclaim 17 wherein the at least one integrated silicon optical componentsunit is configured on a first printed circuit assembly and the quantumdot semiconductor optical amplifier is configured on a second printedcircuit assembly, and wherein the optical connector is a planar opticalconnector.
 19. The network device of claim 17 wherein the at least oneintegrated silicon optical components unit, the optical connector, andthe at least one quantum dot semiconductor optical amplifier are coupledtogether using one or more integrated optical waveguides.
 20. Thenetwork device of claim 17 further comprising at least one integratedcircuit for switching data, wherein the one or more lasers, the at leastone integrated silicon optical components unit, and the integratedcircuit for switching data are co-packaged.
 21. A method of sending dataacross a network comprising: generating an optical signal along atransmission path in one or more lasers; coupling the optical signal toat least one integrated silicon optical components unit in thetransmission path; and coupling the optical signal from the at least oneintegrated silicon optical components unit to at least one opticalconnector configured proximate to at least one socket of a networkdevice chassis, wherein the at least one optical connector is configuredto couple to a pluggable quantum dot semiconductor optical amplifier inthe transmission path to receive the optical signal from the at leastone integrated silicon optical components unit through the opticalconnector and produce an amplified optical signal to an optical fibercoupled to an output of the at least one quantum dot semiconductoroptical amplifier, and wherein the one or more lasers are operable below10 mW per channel.